Various types of machinery support devices have been around for years. In its simplest form, a machinery support consists of one or more machinery feet resting on one or more foundations with one or more fastener assemblies at each location to hold the machinery in place. However, machinery feet and foundations themselves are seldom adequately level and parallel. Thus, machinery support devices are added between each foot and the foundation to allow independent adjustments to be made to compensate for misalignment of the height and parallelism between each foot and the foundation. One prior art device often used was to place machined block shims (not show) between the feet of the supported machinery and the machinery foundation. However, the adjustment process required that the shims be repeatedly machined and checked until adequate support, i.e., alignment of both the height and parallelism, had been achieved. This adjustment process has been laborious and expensive.
Fastener assemblies have been used to attach the machinery feet to the foundation. The fastener assembly fits through an opening (hole) in each of the feet in the machinery, the corresponding support device, and the foundation. The fastener opening can be, and often is, limited as to clearance around the fastener. In the event of a large lateral load such as can be developed due to an external shock, the slip planes between the foot and the shim and between the shim and the foundation will try to slide. The limited clearance around the fastener will prevent significant lateral motion. Thus, the fastener will be stressed in shear only. Fasteners are routinely sized to accept this shear stress without failing.
In addition, the shim is much stiffer than the fastener. With standard preload techniques, the shim carries any cyclic loading (such as can be developed by sea-way motions) thus eliminating fatigue issues.
To resolve the expense with the repeated machine-and-check adjustment process described above, a recent prior art support system has been developed. It is a mechanically adjustable support device, otherwise known as a Viacom mechanically adjustable chock (MAC-V), which is shown in FIGS. 1A-1B. The MAC-V assembly 10 has three separate and distinct parts, a base ring 12, an adjustable riser 14, and a lenticular washer 16 resting on the adjustable riser 14. Base ring 12 is threaded on the inside. The adjustable riser 14 can be threaded into base ring 12 to provide for height adjustment. The height adjustment of the adjustable riser 14 can be locked by using an optional set screw 30.
The adjustable riser 14 and the lenticular washer 16 have mating concave/convex spherical surfaces that permit an angular adjustment between the two parts to compensate for foundation 18 and machinery foot 20 being out-of-parallel. The lenticular washer 16 provides for the ability to compensate for this slight angular misalignment of the foot of the machinery 20 relative to the foundation 18 upon which the machinery rests.
An opening 22 receives a fastener 28 through the lenticular washer 16. In order to prevent interference between the lenticular washer 16 and fastener 28 when the lenticular washer 16 slides sideways to adjust for angular misalignment, the opening 22 is larger than the opening 24 in the adjustable riser 14. This difference in opening sizes results in an unsupported length of fastener equal to the height of lenticular washer 16 between the adjustable riser 14 and the machine foot 20. In addition, when the adjustable riser 14, within the ring base 12, is adjusted upward, there can be an unsupported length of fastener between the foundation 18 and adjustable riser 14 equal to the adjustment height.
One problem with the MAC-V 10 is that in the event of a large lateral load such as may occur during a sudden external shock, the slip planes between the foot 20 and the lenticular washer 16, and between the foundation 18 and the ring base 12 will slide past each other in the same way as the shim, except that since there are long unsupported spans between the related parts, the fastener can develop a significant degree of bending stress at each unsupported span. It has been determined that in order to limit the stress on the fastener 28 in MAC-V 10, to the same degree of as the shim method, the shear load carrying capacity of the MAC-V 10 must be limited by about 45%.
Another problem with the MAC-V 10 is that the stiffness of the joint relative to the stiffness of the fastener is much lower than with the shim support method. When cyclic loading is an issue (as it can be due to sea-way motions on a ship), the fatigue life of the fastener in the MAC-V 10 must be specifically addressed by calculation rather than using a set preload as with the shim. The fatigue life of the fastener may be significantly lessened by comparison to the shim method and the ability to withstand large axial loads is similarly reduced.
The present invention is providing improvements to the MAC-V in order to overcome possible bending stresses and fatigue life to the fasteners.